1. Field of the Invention
The present invention relates to a video endoscope system for fluorescence observations based on autofluorescence emitted from living tissue, and also relates to an illumination optical system used for such a video endoscope system. The present disclosure relates to object matter contained in Japanese Patent Applications No. 2000-254824 (filed Aug. 25, 2000) and 2000-330303 (filed Oct. 30, 2000) which is expressly incorporated herein by reference in its entirety.
2. Description of the Related Art
A conventional video endoscope system photographs images of fluorescence (autofluorescence) emitted from living tissue irradiated by excitation light such as ultraviolet light to enables an operator to observe fluorescence image of the living tissue. The intensity of autofluorescence emitted from diseased living tissue is lower than the intensity of autofluorescence emitted from healthy living tissue. Thus, the operator observing the fluorescence images of the object can recognize a region distinguished by lower autofluorescent intensity as an affected area with high potential for abnormalities.
Such a video endoscope system has a light source unit for alternately emitting visible light and excitation light, a light-guide optical system for guiding emitted visible light and excitation light as illuminating light, respectively, and a CCD for picking up the image of the object illuminated or irradiated by the illuminating light. While the visible light guided through the light-guide optical system illuminates the object, the CCD receives the visible light reflected by an object surface and outputs it as a reference image signal. When the excitation light guided through the light-guide optical system irradiates the object, the object emits autofluorescence, which is then picked up by the CCD and converted into a fluorescence image signal. Based on the reference image signal and the fluorescence image signal, a diagnostic image signal for the object is generated. For example, the fluorescence image signal is subtracted from any one of the three image signals corresponding to the three primary colors which constitutes the reference image signal to generate a diagnostic image signal. The diagnostic image signal causes a display device to display a diagnostic image on its screen. In the diagnostic image thus displayed, a portion of the object that does not emit autofluorescence is displayed as an image identical to that obtained by normal observation (monochromatic image or color image), whereas a portion of the object that emits autofluorescence is displayed as colored, such that the degree of coloring is proportional to autofluorescence intensity, which enable the operator to grasp the shape of the object by observing this diagnostic image and to recognize the intensity of the autofluorescence thereof.
FIG. 23 is a schematic diagram of the light guide optical system and the light source unit that constitute the conventional video endoscope system. As shown in this FIG. 23, the light guide optical system of this video endoscope system includes a light guide fiber bundle consisting of a number of optical fibers tied in a bundle (hereinafter abbreviated to as xe2x80x9clight guidexe2x80x9d) 72 and a light distribution lens 73 for further spreading the illumination light emitted from this light guide 72. The light source unit has a condenser lens 71 for converging the illumination light emitted from a light source lamp (not shown in the figure) onto a proximal end face of the light guide 72. In such a configuration, the light source unit makes the visible light and the excitation light converted into collimated light beams incident on the condenser lens 71, respectively. The condenser lens 71 converges the visible light and the excitation light so that they enters the proximal end face of the light guide at maximum incidence angles xcex1 approximately identical to each other. The light guide 72 emits the visible light and the excitation light through its a distal end face, respectively. The emitted visible light and excitation light are diverged by a light distribution lens 73, respectively, to illuminate the object. Note that the angular aperture of the optical fiber becomes larger as the wavelength of light gets shorter, light guide 72 therefore emits excitation light with a larger angular aperture than that for the visible light. As a result, area xcex4 irradiated by the excitation light through the light distribution lens 73 becomes wider than area xcex3 illuminated by the visible light. As a result, in a portion of the diagnostic image that indicates the area xcex4 irradiated with the excitation light but out of the area xcex4 illuminated with the visible light, the condition of the object is not indicated rightly, which makes it difficult or impossible for the operator to correctly grasp the status of the object based on this diagnostic image.
It is the object of the present invention to provide a video endoscope system by which the area of the object illuminated with the visible light can be made to correspond to that irradiated with the excitation light and to provide an illumination optical system used for such a video endoscope system.
The illumination optical system according to the present invention includes as its components a light guide optical system that has a fiber bundle for emitting a light beam incident on its proximal end face through its distal end, a visible light lamp for generating visible light, a first optical system for collimating the visible light generated by the visible light lamp, an excitation light lamp for generating excitation light that excites living tissue to cause fluorescence, a second optical system for forming the excitation light generated by the excitation lamp into a beam whose diameter is smaller than that of the visible light collimated by the first optical system, a switching mechanism that alternately guides the visible light formed into the collimated light beam by the first optical system and the excitation light formed into the collimated light beam by the second optical system to a common optical path, and a condenser optical system for converging the visible light and the excitation light that are alternately guided by the switching mechanism onto the proximal end face of the fiber bundle.
By that structure, the diameter of the excitation light beam at the condenser optical system is less than that of the visible light. After the excitation light and the visible light being converged through the condenser lens, the maximum incidence angle of the excitation light with respect to the proximal end face of the fiber bundle becomes smaller than that of the visible light with respect to the proximal end face of the fiber bundle. As a result, the divergence angles of the visible light and of the excitation light emitted through the distal end face of the fiber bundle are made to correspond to each other.